In recent years, communication systems using radio signals, such as a mobile telephone system, have been widely used. In communication systems of this type, the frequency of a radio signal received by a receiver shifts from a predetermined frequency in some cases, owing to the fluctuation in oscillation frequency of a frequency oscillator used to cause a transmitter to generate a radio signal having a predetermined frequency. Further, the frequency of a radio signal received by a receiver shifts from a predetermined frequency in some cases, owing to the modulation of the radio signal occurring in a transmission path through which the radio signal is transmitted. To accurately extract data from the received radio signal, therefore, it is desired that the receiver correct a frequency error due to the shift of the received frequency.
In view of the above, a method has been known which, when a radio signal has two periods including the same signal waveform at predetermined time intervals, calculates the frequency error on the basis of the correlation value between respective signals of the two periods. According to an orthogonal frequency division multiplex (OFDM) method, for example, a guard interval (GI) for reducing the influence of multipath is provided at the head of a transmission symbol. The guard interval contains a copy of the signal of a tail end portion of an effective symbol that is a data carrying portion of the transmission symbol. Therefore, with the calculation of the correlation between the guard interval and the tail end portion of the effective symbol in a transmission symbol, the frequency error is estimated as the phase rotation amount of the correlation value.
However, if there is an interference signal, such as a radio signal transmitted from another communication system and having the same frequency range as the frequency range of the intended radio signal, the above-described correlation value includes the correlation value of the interference signal. According to the above-described technique, therefore, the frequency error is not accurately calculated. In view of this, a technique has been proposed which detects the frequency error by subtracting an offset value based on the interference signal, which is calculated from the correlation value between two signal periods included in the period other than the guard interval, from the correlation value between the guard interval and the corresponding effective signal.
The related art includes Japanese Laid-open Patent Publication No. 2002-290371.